This paper is a qualitative and quantitative study. The main purpose of the paper is to diagnose what makes English communication difficult at the Korean EFL adult level. In order to obtain data, this study employed interviews and a questionnaire. We identified thirty three factors blocking pathways to oral communication. Qualitative analysis repeatedly revealed patterns such as lack of grammar, lack of vocabulary, lack of background knowledge, and peer pressure, but quantitative analysis yielded somewhat different results: lack of colloquial expressions, lack of vocabulary, lack of various topics, problems in the educational system, difficulty in using existing knowledge, and lack of grammar. Findings which were common to both qualitative and quantitative analyses suggest that lack of linguistic knowledge and lack of background knowledge are major barriers learners encounter in communication. On the basis of the results, suggestions are made for overcoming these barriers.